This invention relates generally to a fuel delivery system and more particularly to a returnless fuel delivery system.
Electric motor fuel pumps have been used to deliver fuel to engines in a wide range of applications. In some systems, the armature of the electric motor and stator are disposed downstream of a fuel pumping assembly. Fuel is drawn into the pumping assembly and discharged therefrom under pressure into a fuel pump housing such that the fuel flow through the housing is in contact with the electric motor to cool it. In some high heat applications or conditions, this fuel flow through the pump is insufficient to cool the fuel pump. Some prior marine engine fuel systems have tried to supplement the cooling of the pump by installing the pump in a fuel reservoir and then cooling the reservoir with a water jacket through which cool water is circulated.
This fuel reservoir and water jacket system is inadequate in many applications to sufficiently cool the pump. For example, with a speed controlled. fuel pump, such as when a pulse width modulated drive is used to control the operation of the pump and hence, the fuel flow rate delivered from the fuel pump. With such a pulse width modulated drive or other variably controlled fuel pump, at idle or low engine speeds there is a relatively low fuel flow rate through the pump which provides limited cooling of the pump. Excessive heating of the fuel pump can cause vapor formation in the liquid fuel, decreased efficiency of the pump and even failure of the pump in use. Further, the fuel may become heated in different applications causing excessive fuel vapor formation which can cause vapor lock. Accordingly, it is desirable to also cool the fuel in addition to the fuel pump to reduce vapor formation and the likelihood of vapor lock.
A fuel system has a fuel pump controlled and driven by a pulse width modulated drive to deliver fuel to the engine at a rate corresponding to the engine demand and a recirculation cooler or heat exchanger which receives a portion of fuel discharged from the fuel pump, cools that fuel, and then returns the cooled fuel to the inlet of the fuel pump to cool the pump as the cooled fuel flows through the pump. The recirculation cooler is preferably formed of a material of high thermal conductivity and has a coolant passage adjacent to a fuel passage to reduce the temperature of the fuel that flows through the recirculation cooler. Desirably, the cooler fuel provided by the recirculation cooler to the inlet of the fuel pump supplements the cooling of the fuel pump motor and reduces fuel vapor formation in the fuel. In one form, the recirculation cooler comprises a block having passages drilled, bored or otherwise formed therein to define the separate coolant passage and the fuel passage. In another form, the recirculation cooler has a generally cylindrical housing with a coiled tube received in the housing and defining the fuel passage with the coolant passage defined within the interior of the cylindrical housing. In either embodiment, heat from the fuel in the recirculation cooler is transferred to the recirculation cooler material and the cooling water to reduce the temperature of the fuel.
Objects, features and advantages of this invention include providing a recirculation cooler for engine fuel systems which supplements the cooling of the fuel pump, enables use of a pulse width modulated or otherwise variably controlled electric fuel pump, permits use of an electric motor fuel pump in high heat fuel system applications, reduces vapor formation in the liquid fuel, prevents vapor lock of the fuel pump, reduces the temperature of fuel discharged from the fuel pump, and is of relatively simple design, economical manufacture and assembly and in service has a long, useful life.